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Third Party Script Impact Calculator

Quantify the performance cost of third-party scripts.

About Third Party Script Impact Calculator

Third-party scripts cost more than their size suggests, because each new domain adds a full connection setup. Tag managers make it easy to accumulate scripts nobody owns or monitors. Third-party code is the most common cause of poor field performance, and it is often the easiest to remove because much of it is unused.

Formula

Third Party Script Impact

Impact = transfer time + execution time + per-domain connection overhead

connection overhead
Each new domain requires DNS, TCP and TLS, roughly 150 ms

Worked example

With the default values below, Third Party Script Impact Calculator returns Total Performance Impact of 2,736. Change any input above and every figure here is recalculated in your browser.

Inputs used

Number of third-party scriptsminimum 0
12
Average script sizeminimum 0 KB
85 KB
Average execution time per scriptminimum 0 ms
60 ms
Connection speedminimum 0.01 Mbps
10 Mbps
Additional domains contactedminimum 0
8

Results

Total Performance Impact
2,736 ms
Transfer Time
816 ms
Total Execution Time
720 ms
DNS and Connection Overhead
1,200 ms
Verdict
Severe — third-party code dominates load time

Step by step

  1. 1Values used
  2. 2Third Party Script Impact
  3. 3Total Performance Impact= 2,736 ms
  4. 4Transfer Time= 816 ms
  5. 5Total Execution Time= 720 ms
  6. 6DNS and Connection Overhead= 1,200 ms
  7. 7Verdict= Severe — third-party code dominates load time

Assumptions and limits

  • The result is derived only from the 5 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to whole numbers, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is Third Party Script Impact calculated?

Impact = transfer time + execution time + per-domain connection overhead Third-party scripts cost more than their size suggests, because each new domain adds a full connection setup. Tag managers make it easy to accumulate scripts nobody owns or monitors.

Why does Third Party Script Impact matter?

Third-party code is the most common cause of poor field performance, and it is often the easiest to remove because much of it is unused.

What values do I need to enter?

This calculator takes 5 inputs: Number of third-party scripts, Average script size, Average execution time per script, Connection speed, Additional domains contacted. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.

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